This invention relates to granular material spreading devices which employ a marking means to delineate the path of travel of the spreader over a surface. Examples of such devices may be found in U.S. Pat. Nos. 927,518; 2,199,421; 3,019,470; 3,114,481; and 3,443,727.
Most of the prior art devices are characterized by the employment of powdered, granular or liquid marking material and the disposition of the marking apparatus relative to the wheels of the ground driven hopper, rather than the hopper opening, which is a more accurate indication of the area upon which the contents of the hopper have been spread.
Some of the deficiencies inherent in the prior art devices have been: the large amounts of marking material required by the continuous flow marking apparatus; a tendency of the granular and powdered marking material to become packed or caked together, thereby clogging the supply outlet and rendering the marker useless; the requirement for dual marking material dispensers with complicated or cumbersome mechanical controls to alternate the marking material supply when the spreader begins a return pass; and the failure of the designers to position the outlets of the material dispensers so that they coincide with the outermost ends of the spreader hopper outlet, to name but a few.
Some additional complaints concerning the prior art devices have been: the high visibility for extended periods of time of the marking material on the surface it contacted; the trouble, bother and mess associated with filling the marking material supply container, and the overall general complexity of the procedure which causes many owners to abandon their marking apparatus after a limited number of uses.